1. Field of the Invention
This invention deals with the formation of plastic materials and, more particularly, is in the field of forming plastic components such as decorative plastic sheets which incorporate lamellae. Still more particularly, this invention is in the field of plastics incorporating lamellae, such as nacreous lamellar material of the type which, in order to impart to the plastic a decorative appearance or effect, must be aligned in a particular manner, normally with the broad faces of the nacreous crystals paralleling the surface of the plastic material which is to be viewed.
2. The Prior Art
It is known to provide plastic materials having simulated pearl or mother-of-pearl effects by incorporating within a transparent plastic mass, a nacreous material, such as fish scales, basic lead carbonate crystals or the like. The fish scales or lead carbonate crystals comprise generally flake-like lamellae which, when disposed in random orientation within the plastic menstruum, give no special pearly or decorative effect.
It is further known that when the flake-like materials are oriented with their broad surfaces perpendicular to the angle at which the plastic is to be observed, the plastic takes on a sheen or luster reminiscent of pearl or mother-of-pearl.
The effect is not limited to the production of a pearly appearance since it is known that other flake-like additives, such as silica flakes, aluminum flakes, etc., when their broad surfaces are aligned with the surface of the plastic material or oriented in some other desired selected manner, will enhance the appearance of the plastic.
Numerous means have been suggested for inducing the desired orientation of the lamellae within the liquid plastic mass. Such orientation methods include flowing the plastic mass across a stationary surface or along the inner surface of a rotating drum, extruding the plastic, wiping the surface of the plastic as with a roller, and variations of the foregoing. Other means, such as the creation of electrostatic fields, have been employed for achieving the desired disposition of the particles.
While all of the foregoing methods of orientation are generally satisfactory in that a selected orientation is achieved in the liquid state, great difficulty has heretofore been experienced in obtaining a finished plastic product in which the nacreous flakes are captured in the optimum position achieved during the orienting step.
I have determined that part of the difficulty in prior methods for making ornamented plastics of this sort lies in the fact that the curing steps heretofore employed in such methods have the inherent drawback of disorienting the nacreous material. Where heat is employed as the curative step, turbulence created by the heat and reduction of viscosity upon application of heat result in transfer of the material from its optimum oriented position.
Where the material is oriented by flowing into glass cells, for instance, the gravitational effect and Brownian movement produce significant modfications of the pearl position.